1. Technical Background
The present invention relates generally to medical devices, and more particularly to a balloon catheter and stent delivery system.
2. Discussion
The present invention involves a balloon catheter for inserting a stent, vascular scaffold, or other medical device to a desired site in a patient for medical treatment. The balloon is specially shaped with structural features for cooperating with corresponding stent designs to enhance stent retention.
For purposes of brevity, the following background and description will focus generally on the example of a medical device delivery system, in which the medical device is a stent, and the delivery system is based on a balloon catheter. Of course, other medical devices and other delivery systems that are within the scope of one of the Claims below are included in the present invention.
It is desirable to provide a novel combination stent delivery system, along with a unique manufacturing process, having an optimum arrangement of several features. These desirable features include a tendency to retain the stent in position on a deflated balloon, small initial size or profile, bending flexibility, column stiffess or pushability, pull strength, inflation strength (sometimes referred to as “rated burst pressure”), etc.
To provide an optimum arrangement of these features, the present invention recognizes and takes advantage of structural aspects of certain stents, such that the delivery system optimizes stent retention without compromising any of the other performance qualities.
Among the stent structural features that may be utilized by the present invention are an expandable cylindrical mesh or lattice, stents are preferably designed to be flexible during delivery and bend along a vascular path. One design that allows such flexibility is to include a series of main elements for hoop strength, preferably coupled by a series of flexible links to enhance flexibility. The stent should preferably also have an optimum selection of features, including flexibility, small profile, hoop strength when expanded, and resilience, etc.
Accordingly, stent delivery systems of the present invention provide balloons for delivery and expanding the stent, in which the balloon has a deflated shape with a pattern of ridges or bumps. These ridges or bumps tend to increase stent retention during delivery, and preferably cooperate with the pattern of main stent elements and flexible links, to better hold the stent in place on the catheter delivery system.
Background:
Balloon catheters are used in a variety of therapeutic applications, including intravascular catheters for procedures such as angioplasty treating coronary, neurological and peripheral blood vessels partially or totally blocked or narrowed by a stenosis. By way of example, the present invention will be described in relation to coronary and peripheral angioplasty treatments. However, it should be understood that the present invention relates to balloon catheters and stent delivery systems generally, and is not limited to the specific embodiments described herein.
Most balloon catheters have a relatively long and flexible tubular shaft defining one or more passages or lumens, and an inflatable balloon attached near one end of the shaft. This end of the catheter where the balloon is located is customarily referred to as the “distal” end, while the other end is called the “proximal” end. The balloon is connected to one of the lumens extending through the shaft to selectively inflate and deflate the balloon. The other end of this inflation lumen leads to a hub coupling at the other end for connecting the shaft lumens to various equipment. Examples of this type of balloon catheter are shown in U.S. Pat. No. 5,304,197, entitled “Balloons For Medical Devices And Fabrication Thereof,” issued to Pinchuk et al. on Apr. 19, 1994, and also in U.S. Pat. No. 5,370,615, entitled “Balloon Catheter For Angioplasty,” issued to Johnson on Dec. 6, 1994.
A common treatment method for using such a balloon catheter is to advance the catheter into the body of a patient, by directing the catheter distal end percutaneously through an incision and along a body passage until the balloon is located within the desired site. The term “desired site” refers to the location in the patient's body currently selected for treatment by a health care professional. A larger guiding catheter may often be used to access the local area near the desired site, providing a smooth, supported lumen for conducting other devices including balloon catheters to the desired site. After the balloon is within the desired site, it can be selectively inflated to press outward on the body passage at relatively high pressure to a relatively constant diameter, in the case of an inelastic or non-compliant balloon material.
This outward pressing of a constriction or narrowing at the desired site in a body passage is intended to re-open or dilate that body passageway or lumen, increasing its inner diameter or cross-sectional area. When performed in a blood vessel, this procedure is called “angioplasty.” The narrowing of the body passageway lumen is called a lesion or stenosis, and may be formed of hard plaque or viscous thrombus. The objective of this angioplasty procedure is to treat the lesion by increasing the cross-sectional area of the blood vessel, to encourage greater blood flow through the newly expanded vessel.
Unfortunately, the lumen at the angioplasty site may re-close or become narrow again. This possible phenomenon is called restenosis, and may occur in a certain percentage of percutaneous transluminal angioplasty patients. Restenosis may require an additional procedure, such as another angioplasty, drug therapy treatment, or even surgery including bypass graft.
Stents:
In an effort to prevent restenosis, a short flexible cylinder or scaffold made of metal or polymers, referred to as a stent, may be permanently implanted into the vessel to hold the lumen open, to reinforce the vessel wall and improve blood flow. In 1998, coronary stents were placed in an estimated half million patients in the United States. The presence of a stent tends to successfully keep the blood vessel open longer, but their use may be limited by various factors, including size and location of the blood vessel, a complicated or tortuous vessel pathway, etc. Also, even a vessel with a stent may eventually develop restenosis.
One type of stent is expanded to the proper size at the desired site within the lesion by inflating a balloon catheter, referred to as “balloon-expandable” stents. Balloon-expandable stents are crimped or compressed onto a deflated balloon, to a diameter during delivery that is smaller than the eventual deployed diameter at the desired site.
However, friction forces during delivery may tend to cause a crimped stent to slip in a proximal direction while the catheter system is advanced, or possibly to slip in a distal direction if the physician decides to withdraw the stent without deploying it. It is of course desirable to retain the stent in the proper position during movement, both advancement along a vascular path to the desired site, as well as, subsequent removal if necessary.
In addition, it is desirable to provide a stent delivery system with greater stent retention, that is more capable of holding the stent in position, or also of advancing a crimped stent across a previously deployed stent, or possibly withdrawing it into a guiding catheter.
Drug Delivery:
The present invention is preferably used with a stent or other medical device that may be provided with one or more coatings, to achieve even greater effectiveness. Such coating or coatings may be selected among various coatings, including therapeutic coatings such as anticoagulants, antiproliferatives, or antirestenosis compounds.
For example, a preferred coating for a stent is an anticoagulant coating such as heparin. Another preferred coating is an antirestenosis compound, such as for example rapamycin (which is also known as sirolimus). Such a compound can be very effective at resisting a vessel from re-closing. Any particular coating or type of coating may of course be used independently or in conjunction with any one or more coatings, as desired.
Some pioneering research in drug-coated stents has been conducted, and is described in the following publications, all of which are assigned to Cordis Corporation and are incorporated herein by reference: (i) European Patent Application number EP 99/302918 A2, entitled “Stent With Local Rapamycin Delivery” by Wright et al., filed on Apr. 15, 1999; (ii) PCT Patent Application number US0115562, entitled “Delivery Devices For Treatment Of Vascular Disease” by Falotico et al., filed on May 14, 2001; and (iii) PCT Patent Application number US0115564, entitled “Drug/Drug Delivery Systems For The Prevention And Treatment Of Vascular Disease” by Falotico et al., filed on Oct. 14, 2001.
Accordingly, it is an object of the present invention to provide balloon catheter systems for enhanced position retention of a stent or other medical device during longitudinal movement of the catheter.
It is a further object of the present invention to provide methods for making balloon catheter systems having enhanced position retention of a stent or other medical device.
It is a further object of the present invention to provide methods for making balloon catheters for enhanced stent position retention.
These and various other objects, advantages and features of the invention will become apparent from the following description and claims, when considered in conjunction with the appended drawings.